Just as with skin, the colour of hair is determined by the amount of melanin in the outer layer (cortex) of each hair. Melanin is a protein that has colour. Black hair has the greatest amount of melanin. White hair has no melanin. Hair gets its colour from the two types of melanin that create the variety of hair colors we see.

Eumelanin (sometimes called black/brown melanin) is the darkest melanin and the most commonly found in humans. Phaeomelanin (sometimes called red melanin) is the lighter melanin. One's hair color is the ratio of eumelanin to phaeomelanin. A high amount of eumelanin with little phaeomelanin results in black or brown hair. As the ratio of eumelanin to phaeomelanin lessens, the result is red, ginger, and blonde hair.

This ratio varies enormously among humans. This is why everyone's hair is just a little different.

Melanin is produced by a group of specialized cells called melanocytes. These cells are located near the hair bulb. They collect and form bundles of a pigment protein complex called melanosomes. The size, type, and distribution of the melanosomes will determine the type of melanin produced and in which ratio. The type of melanin of a person's hair is inherited.

Melanin also varies in the hair of different parts of the body. This is why pubic hair is sometimes a slightly different colour from hair elsewhere. The absence of melanin later in life causes white hair. White hair may appear on some parts of the body before others because there is variation in this too.

Interesting facts

The average human hair is 91 per cent protein.

The average human hair is composed of 45 per cent carbon, 27.9 per cent oxygen, 15.1 per cent nitrogen, 6.6 per cent hydrogen, and 5.2 per cent sulfur.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to [email protected]